Are You Really Worth $428 to Facebook?

Since some people are speculating that Facebook’s valuation might be 15 Billion dollars, and there are 34 million active users (by last estimate I could find), that equals to $428 per user. Can that be a realistic lifetime value of an average Facebook user?

I know this is an oversimplification, but it is still a way to look at the staggering number in terms of one of Facebook’s most valuable metrics.

What is the average lifetime value of a Google user? Does anyone have any idea?

Maybe it all makes sense in the end, but when you’re throwing these sort of valuations around for websites (whose visitors tend to be historically fickle) it starts sounding a little crazy.